The present invention relates to an automotive radar system having an oscillator, which generates a high-frequency signal only in intervals during operation of the radar system as a function of a control signal, and a microwave diode, in particular a Gunn diode or an Impatt diode accommodated inside a casing-like body.
A generic radar system is described in International Patent Publication No. WO 97/02496, for example. This document describes a monostatic FMCW radar sensor for a motor vehicle for detection of objects, with at least one antenna feed in combination with a dielectric lens being designed for both sending and receiving a suitable echo signal. This generic radar system is described in greater detail below with reference to FIGS. 1 and 2. According to International Patent Publication No. WO 97/02496, the output power of the oscillator can be blanked out to reduce the average energy consumption or, in other words, to reduce the average microwave output power emitted. In this regard, the operating mode of this FMCW radar sensor approximates that of a pulse radar. In a concrete application, the oscillator is blanked out in a clock ratio of 90 milliseconds pause to 10 milliseconds transmission time, for example.
With this radar sensor, oscillator 5 according to FIG. 4 is connected in series to a control transistor 40, forming a voltage divider with it. It is known that the instantaneous oscillation frequency can be influenced within a certain range by operating voltage Uosz on the oscillator, so it is possible to control both the frequency modulation and the blanking out of the oscillator by way of the transistor. There is usually no voltage applied to the oscillator during the blanking out period, and no current flows through the voltage divider accordingly.
Problems occur when the oscillator contains a microwave diode as in the present case. Such oscillators based on semiconductor components have the property of little or no response at very low temperatures, in particular below xe2x88x9220xc2x0 C., which can easily occur with use in a motor vehicle. This is true in particular because due to the clocked operation, self-heating of the oscillator is not sufficient to guarantee a reliable response at a precise frequency in this case. One possible way to eliminate this disadvantage would be to keep the oscillator in constant operation at such low temperatures. However, this would lead either to greater environmental pollution because of the increased average total output power or to a greater expense to prevent this increased pollution. The oscillation frequency of the oscillator in this operation can also drift so far away that the frequency control circuit is no longer capable of pulling it back into the allowed range. Thus, the oscillator cannot be safely prevented from oscillating outside the narrowly defined allowed range in this type of operation.
Another possibility is to heat the oscillator with the help of a heating resistor at very low temperatures. However, this also requires additional wiring and thus higher costs.
An object of the present invention is to provide an automotive radar system which guarantees a reliable and secure oscillator response in a simple and inexpensive manner even at very low temperatures and in clocked operation.
This object is achieved according to the present invention by a radar system with which at least one of the components, an ohmic resistor, transistor or IC is arranged so that is in contact with the casing-like body or an element thermally connected to the latter, with this component within the circuit configuration of the radar system having at least one other function in addition to generating heat. optionally, an electrically insulating heat transfer film or paste or a comparable material may be provided for electric insulation between the component and the casing-like body or the element thermally linked to it. This is also included in the formulation given above, because ultimately it is important only that the respective component is thermally linked to the oscillator. The element thermally connected to the casing-like body may be, for example, a hollow conductor extension of the oscillator or a heat sink.
It is especially advantageous if the component is mounted on the casing-like body or the element thermally connected to it.
In a preferred embodiment of the present invention, the component is a transistor which is used as a controlling means for adjusting the size of the control signal of the oscillator.
An advantage of the radar system according to the present invention is that self-heating of the oscillator is increased very inexpensively, because no additional components or circuitry measures are required. In addition, no additional heating energy is necessary, so there is no change in the power consumption of the radar system according to the present invention in comparison with known systems. Nevertheless, a reliable response of the oscillator at an accurate frequency is guaranteed even at very low temperatures on the basis of the present invention. In comparison with continuous operation of the oscillator at very low temperatures, which is also conceivable as an alternative, the average microwave power emitted is reduced significantly.
Furthermore, there is the possibility of heating the oscillator at very low temperatures even when the radar system itself is not yet in operation, e.g. because the driver does not yet need the related function. The oscillator is advantageously heated as soon as the engine is started at very low temperatures, as explained in greater detail below on the basis of the following embodiments. However, start-up of the radar system is allowed only when the minimum required operating temperature of the oscillator has been reached. This lasts only approximately. one to two minutes with the option proposed here.